Drill strings are usually supported by spiders that fit in the opening of the rotary table. They usually have a slip bowl in which slips are peripherally distributed to surround pipe to be gripped. The slip bowl opens upwardly. When a pipe string suspended in the well is to be gripped by the spider, the slips are moved downward. The slip bowl surface urges the downwardly moving slips to move radially inward to bear upon, and grip, the pipe. When the slips grip pipe loads, the resulting downward force adds to the radially inward thrust of the slips, and largely defines the essential elements of what has become known as the fail safe system. Teeth carried by the slips contact the pipe to improve pipe security. The teeth may be on detachable dies that are carried by the slips.
Spiders are currently sold as an assembly which is inserted into the rotary table opening. Considerable design and engineering work has gone into the slip manipulation gear related to spiders. The spider housing, in effect, duplicates the function of the rotary table structure.
Larger tubulars, such as casing, are usually handled by spiders that rest on the rig floor above the rotary table. Such spiders are often capable of serving as elevators. The novel slip carriers and slip powering apparatus of this invention can be applied to such spider structures with minimum preparation.
Slips have to be secured to retain, or control, their peripheral distribution within the slip bowl. The slip control structure and slip manipulation gear makes up a considerable part of the usual spider. Such a composite spider can often function with minor, or no, adaptation as an elevator. In some cases, there is no way to distinguish a spider from an elevator.
Spiders and elevators, in many cases, have no power actuators and are strictly manual in operation. When composite spiders are prepared by the manufacturer for use in the field, they have limited adaptability to function for a variety of pipe sizes and, if considerable diversity of use is planned, several spiders have to be on hand or readily available. There is a need for spider sub-assemblies that can be fitted into rotary tables, or related structure, to enable adaptability not currently practical.